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BACKGROUND: Active surveillance (AS) is becoming increasingly employed to manage patients with low risk, gland confined prostate cancer. A barrier to widespread adoption of AS has been the early failure of a small but significant number of patients, often attributed to under sampling of initial prostate biopsy. Prostate MRI (pMRI) has been proposed as an adjunct to aid in identifying cancers that are more extensive than indicated on routine initial biopsy sampling. We sought to determine how pMRI when performed at entry onto active surveillance, influenced progression of patients to treatment due to discovery of greater cancer severity than indicated by other measures.
METHODS: Informed consent was obtained from the appropriate institutional review boards. Our prostate biopsy and active surveillance databases were queried to identify 231 men diagnosed with Gleason score 3+3 prostate cancer on biopsy, clinical stage ≤T2a and had a PSA <20 between June 2005 and September 2012. These men were considered eligible for active surveillance. A retrospective chart review was performed to identify 110 patients who underwent prostate MRI at the time of cancer diagnosis. Prostate MRI was performed in a 1.5T or 3T scanner with an endorectal coil, including multiparametric imaging sequences. We then identified the frequency with which pMRI rendered patients ineligible for AS. Prostate MRI evidence of stage T3 or greater disease was considered the only absolute indication to classify men as ineligible for AS.
RESULTS: We identified 110 patients with biopsy proven low grade, organ confined disease who underwent pMRI as part of their work up. Mean age was 61 years, mean PSA 4.8, and mean prostate volume 44.8 ml. MRI demonstrated a tumor in 77/110 (70%). MRI stage was Tx (not able to assign stage) in 15 (13.6%), T0 in 18 (16.4%), T2a in 36 (32.7%), T2b in 3 (2.7%), T2c in 34 (30.9%), T3a in 1 (0.91%) and T3b 3 (2.7%). An additional 11 (10%) of the patients with stage T2 disease had findings concerning for but not definitive of extracapsular extension (ECE). All 4 patients with T3 disease underwent definitive therapy. Three of the patients with stage T3 disease underwent radical prostatectomy and the fourth underwent radiation therapy. One patient had MRI stage T3a confirmed on prostatectomy and Gleason score upgraded from 3+3 to 4+3. One patient with MRI stage T3b had stage T3a on prostatectomy and Gleason score upgraded from 3+3 to 3+4. The last patient with MRI stage T3b disease had stage T2c on prostatectomy and Gleason score 3+3 confirmed. Of the 11 patients with findings equivocal for ECE, 3 underwent prostatectomy. MRI stage T2 was confirmed in all 3 prostatectomy specimens and Gleason score was upgraded to 3+4.
CONCLUSIONS: Prostate MRI in patients with prostate cancer eligible for AS identifies stage T3 disease or disease concerning for stage T3 in a significant number of patients, potentially altering clinical management. Further study is warranted to validate the clinical impact of these findings, and to determine the timing and cost-benefit of pMRIs in patients on AS.